This invention relates generally to thin film electronic imager devices and more particularly to a low noise solid state radiation imager having repairable defects between an upper conductive layer disposed and underlying components in the imager array.
Solid state radiation imagers typically have a scintillator coupled to a photosensor imager array such that incident radiation of the type to be detected is absorbed in the scintillator, resulting in the generation of light, which in turn is detected by the photosensor array. The imager array typically comprises a number of components (such as photodiodes and switching transistors) which are coupled to address lines for conducting electrical signals to and from individual components in an imager device. A common electrode is disposed over the photosensor array to provide the common contact for each photosensor pixel in the array. The electrical signals generated by the photosensors correspond to the number of detected photons passing from the scintillator, and the signals from the respective photosensors are used to reproduce electronically an image corresponding to the photons detected by the array of photosensors.
A defect in the photosensor array can adversely affect overall performance of the thin film imager device. Common defects include electrical shorts between different components in the array, such as between the common electrode and underlying components (e.g., address lines or switching transistors), or between respective fi underlying components in the array (e.g., between a scan address line and a data address line). The components in the army are commonly formed in a series of steps in which layers of conductive, semiconductive, and insulative materials are deposited and these layers are patterned to form the desired components; unwanted conductive paths, or defects, can result from conductive debris left from the fabrication steps.
Given the expense of fabricating thin film electronic imager devices, it is desirable to have devices that are repairable. In particular, it is desirable to have a device that is repairable after deposition of the common electrode, that is, after the fabrication of the array, at which time tests can be run to check the electrical operation of the array. Any repairs made at this point typically require that the common electrode must be breached (that is, removed to gain access to underlying components that require repair). Particularly for medical imagers, in which noise is a critical factor, it is important that the repaired area not have significant residual electrical leakage that causes noise in the imager array. One problem with repairs of low noise imagers, however, is that repairs that involve breaking through the common electrode often result in leakage paths between the common electrode and underlying components that increase the noise in the array. This electrical leakage can result in noise of sufficient magnitude to degrade the performance of the array to the point where the array does not meet the specifications for use in a radiation imager.
It is accordingly an object of this invention to provide a method of repairing a thin film solid state imager device having an upper conductive layer (common electrode) that provides a low-electrical leakage repair area that does not adversely affect array noise characteristics.
Another object of this invention is to provide a repair method and repair structure that increases yield of fabrication.
A still further object of the present invention to provide an efficacious thin film solid state imager device low-leakage repair structure.